1. Field of the Invention
The present invention relates to a panel for a cathode ray tube (CRT). More particularly, the present invention relates to a CRT panel and a method for manufacturing the same in which the entire area of a viewing screen is uniformly illuminated.
2. Description of the Related Art
Cathode ray tubes generally comprise a panel defining a front exterior of the CRT, and a funnel joined to the panel to define a rear exterior of the CRT. The funnel includes a neck formed on an end of the funnel opposite to the end joined to the panel, and an electron gun provided in the neck of the funnel. The panel includes a display portion defining a distal end of the panel, a curved lateral wall that extends toward the funnel to be joined to the same, a phosphor screen provided adjacent to the display portion within the CRT, a mask frame connected to the lateral wall of the panel, and a shadow mask joined to the mask frame at a predetermined distance from the phosphor screen. The electron gun radiates red (R), green (G) and blue (B) electron beams in a direction toward the panel. The RGB electron beams are controlled by image signals such that the beams are deflected to specific pixels by an electrical field generated by a deflection yoke. The deflection yoke is disposed on an outer circumference of the funnel. The deflected electron beams pass through apertures of the shadow mask to land on specific RGB phosphor pixels of the phosphor screen such that color selection of the electron beams by the shadow mask is realized. Accordingly, the RGB phosphors of the phosphor screen are illuminated for the display of color images.
FIG. 7 illustrates a conventional shadow mask 1 having apertures 3 formed therein, wherein a space between each of the apertures 3 increases toward a periphery of the shadow mask 1. That is, the positions of the apertures 3 on the shadow mask 1, where the electron beams land, become spaced further apart toward outer edges of the shadow mask. This configuration corresponds to incremental increases in the degree of deflection of the electron beams by the deflection yoke toward the periphery of the shadow mask 1. Without this structure, the electron beams would pass through their designated apertures 3 at the center of the shadow mask 1, but not at the peripheries.
With the formation of the shadow mask as in the above, however, the RGB phosphor pixels on the phosphor screen must also be formed in their dot or stripe matrices with spaces corresponding to the spaces formed between the apertures of the shadow mask. Accordingly, the area of a light-absorbing black matrix layer formed between the dot- or stripe-type phosphor pixels enlarges such that brightness is reduced toward the periphery of the display portion.
Therefore, the illumination over the surface of the viewing screen becomes uneven with the center of the viewing screen being brighter than the outer peripheral portions. Assuming that the degree of darkness at the center of the phosphor screen is indexed at 100, the degree of darkness at the periphery of the phosphor screen is 120. In the stripe-type CRT, this translates into a 50% reduction in brightness at the periphery of the display, whereas in the dot-type CRT, this results in a 30% decrease in peripheral brightness.
Meanwhile, the CRT is internally kept in a high vacuum state of 10xe2x88x927 torr or less and, therefore, stress may concentrate on the periphery of the panel. In order to prevent such stress concentration, the thickness of the panel at the periphery is larger than that at the center. With the thickness increasing toward the periphery of the panel, the light transmission of the panel becomes gradually reduced toward the periphery of the panel so that the difference in brightness between the center and the periphery of the panel is significant.
Further, as CRTs become flatter, following advances made in CRT technology, the above problem worsens. Specifically, differences in the spaces between the apertures of the shadow mask from the center to the periphery of the shadow mask, and therefore the spaces between the phosphor pixels of the phosphor layer, or differences in the thickness between the center and the periphery of the panel, increase as the CRT becomes flatter.
The present invention has been made in an effort to solve at least some of the above problems.
It is a feature of an embodiment of the present invention to provide a CRT panel and a method for manufacturing the same in which the entire area of a viewing screen is uniformly illuminated.
In order to provide for the above feature, the present invention provides a CRT panel that includes a display portion defining a distal end of the panel, a curved lateral wall extending from the display portion toward the funnel having an end joined to a funnel, and a phosphor screen formed on an inner surface of the display portion. The phosphor screen has RGB phosphor pixels and a black matrix layer between the RGB phosphor pixels. The CRT panel is provided with a light transmission compensating member for compensating for differences in brightness of the phosphor screen. The light transmission compensating member is positioned on an outer surface of the display portion while varying light transmission at the center and the periphery of the display portion.
The CRT panel may have a flat surface corresponding to the outer surface of the display portion, and a curved surface corresponding to the inner surface of the display portion. Furthermore, the CRT panel may be formed with a dark-tinted clear glass, a semi-tinted clear glass, or a clear glass.
The ratio of light transmission of the center to the periphery of the light transmission compensating member is preferably established to be in the range of 0.7-0.9:1. Preferably, the panel has total light transmission in the range from 30 to 60%, and more preferably in the range of 38 to 55%.
The light transmission compensating member is formed with a tinted coating layer colored such that the tinted coating layer is dark at a center and gradates increasingly lighter toward a periphery thereof. The tinted coating layer contains a coloring agent selected from metallic oxide, metallic colloid, conductive polymer, coloring pigment, or mixtures thereof.
The metallic oxide is selected from SnO2, SbO2, In2O3, indium tin oxide (ITO) and antimony tin oxide (ATO) or mixtures thereof. The metallic colloid is selected from Ag, Pd, Au, Ru, Pt, Rh, As, or mixtures thereof. The coloring pigment is selected from carbon black, titan black, graphite, cobalt oxide, nickel oxide, or mixtures thereof. The conductive polymer is selected from polythiophene, polypyrrole, or mixtures thereof.
The amount of the coloring agent in the tinted coating layer is established to be in the range of 0.1 to 1 wt %.
An antistatic coating layer, an antireflection coating layer and a non-glare layer may be sequentially formed on the tinted coating layer.
These and other features and advantages of the embodiments of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.